1. Field of the Invention
The present invention relates generally to packers for use in oil and gas wells for providing annular seals between the outside of pipe and the surrounding surface of the borehole or casing, and more particularly to inflatable packers having long inflatable sleeves adapted to be inflated with a cement slurry, having means for increasing the friction between the pipe and the inflatable sleeve.
2. Description of the Prior Art
Inflatable packers of the type disclosed, for example, in U.S. Pat. No. 3,604,732, or U.S. Pat. No. 3,837,947, have been used for many years. Such packers include a tubular mandrel that is covered by an inflatable sleeve secured to the mandrel by a pair of axially spaced apart collars. The sleeve is normally reinforced by a reinforcing sheath, which comprises a plurality of overlapping ribs connected between the collars. Valve means are provided for allowing inflating fluid to enter between the exterior of the mandrel and the inflatable sleeve to inflate the sleeve into sealing contact with the wellbore or casing. Such inflatable packers function to isolate the annulus above the packer from that below and, accordingly, need to be only of a length long enough to form an effective seal.
More recently, there have been developed inflatable packers for use in well completion, which are adapted to be positioned adjacent the producing zone and inflated with cement. After the cement has set, the packer is perforated and the well is produced through the packer. Examples of such inflatable packers are disclosed, for example, in U.S. Pat. No. 3,918,522, U.S. Pat. No. Re. 30,711, and U.S. Pat. No. 3,907,034. Such inflatable packers tend to be relatively long, i.e. from 10 feet to 40 feet in length, in order to seal against both the producing formation, which is perforated, and the formations above and below the producing formation.
Since the completion type inflatable packers are of such length, the central portion of the inflatable sleeve is supported and, in effect, reinforced by the borehole. Accordingly, a reinforcing sheath is unnecessary in the central part of the inflatable sleeve. However, reinforcing is necessary adjacent the ends of the inflatable sleeve to prevent the inflatable sleeve from extruding past the securing collars or blowing out. Therefore, the inflatable sleeves of the completion type packers are normally reinforced only at the ends adjacent the securing collars.
As inflatable packers are run into the borehole, there is sometimes contact between the inflatable sleeve and the borehole wall. Such contact is particularly likely in deviated holes. Contact between the sleeve and the borehole wall during movement causes frictional forces to be applied to the sleeve that tend to move the sleeve with respect to the mandrel. In short length inflatable packers with continuous reinforcing sheaths, the reinforcing sheath provides a measure of stiffness to the sheath which prevents axially movement due to frictional wellbore contact. However, in the case of long packers with largely unreinforced inflatable sleeves, when the coefficient of friction between the wellbore and the sleeve exceeds the coefficient of friction between rubber and the mandrel, the sleeve can move with respect to the mandrel. Such movement can cause thickening of the sleeve at the upper end of the inflatable packer and can deform outwardly the upper reinforcing material, in some instances, the movement of the sleeve along the mandrel can cause the diameter of the packer to become greater than that of the borehole, in which case the packer becomes stuck.
A solution to the problem of movement of the inflatable sleeve with respect to the mandrel is provided in U.S. Pat. No. 4,311,314, which discloses an inflatable packer having an inflatable sleeve mounted on a tubular mandrel that is covered with a gritty sand paper-like material. The grit particles are bonded to the outer surface of the mandrel by a suitable binder, such as an epoxy resin, as for example the adhesive sold under the trademark EPON by Shell Chemical Corporation. The coefficient of friction of the inflatable sleeve on the grit covered surface is much higher than the coefficient of friction between the inflatable sleeve and a borehole wall. Accordingly, the improvement of U.S. Pat. No. 4,311,314, very effectively solves the problem of the movement of the inflatable sleeve with respect to the mandrel.
However, there has been developed recently, new cement bond log equipment that is gaining substantial industry acceptance. Unfortunately, epoxy resin acoustically decouples steel from cement. While the bond between the mandrel and the epoxy and between the epoxy and the cement may be perfectly good, the new cement bond logging equipment indicates that proper bonding has not been achieved.
It is therefore an object of the present invention to provide an inflatable packer having a high coefficient of friction between the mandrel and the inflatable sleeve without including a grit like coating.